This invention relates to an arrangement of components mounted on a circuit board for use in a radio apparatus.
The conventional radio apparatus has a plurality of circuits mounted on a circuit board 1 as shown in FIG. 3. This circuit board 1 has dimensions of, for example, 80 mm.times.57 mm.
First, the construction and operation of the receiver section of the radio apparatus will be described. Referring to FIG. 3, a high-frequency signal received by an antenna 2 is supplied through a low-pass filter 3 and through an antenna switch 4 to a band-pass filter 5 where its frequency band is limited. The signal from the band-pass filter 5 is amplified by a high-frequency amplifier 6, and then supplied to a band-bass filter 7 where its frequency band is further limited. The signal from this band-pass filter 7 is supplied to a first mixer 8. On the other hand, a data signal indicating a frequency division ratio or the like which determines the oscillation frequency, i.e., an oscillation frequency specifying signal 22, is supplied to a phase-synchronization loop circuit 19 through a connector 21 from another circuit board (not shown) on which an audio signal circuit and a control circuit are mounted. The phase-synchronization loop circuit 19 responds to the signal 22 to control the oscillation frequency of a first local oscillator 18. The output signal from the first local oscillator 18 is supplied to the first mixer 8. The high-frequency signal fed to the first mixer 8 is thus converted into a first intermediate frequency signal having a certain lower frequency. The circuits from the low-pass filter 3 to the first mixer 8 constitute the receiver's high-frequency section for receiving the high-frequency signal.
The first intermediate frequency signal from the first mixer 8 is supplied to a band-pass filter 9 where its frequency band is limited. The band-limited signal from the band-pass filter 9 is amplified by a first intermediate frequency amplifier 10, and then supplied to a second mixer 11. The second mixer 11 is also supplied with a signal from a second local oscillator 12, and thus the first intermediate frequency signal is converted to a second intermediate frequency signal having a still lower frequency. The frequency band of the second intermediate frequency signal is by a band-pass filter 13, amplified by a second intermediate frequency amplifier 14, and then demodulated by a demodulator 15. The demodulated signal 24 is output from the circuit board 1 through the connector 21. The circuits from the first mixer 8 to the demodulator 15 constitute the receiver's intermediate frequency section for handling the intermediate frequency signals. Particularly the circuits from the first mixer 8 to the second mixer 11 constitute a first intermediate frequency section for handling the first intermediate frequency signal, and the circuits from the second mixer 11 to the demodulator 15 constitute a second intermediate frequency section for handling the second intermediate frequency signal.
The construction and operation of the transmitter section of the radio apparatus will now be described. Referring to FIG. 3, the oscillation frequency of a carrier-wave oscillator 20 is controlled by the phase-synchronization loop circuit 19 in response to the oscillation frequency specifying signal 22 which is supplied through the connector 21. A carrier signal generated in the carrier-wave oscillator 20 is modulated by a modulation signal 23 which is supplied through the connector 21. Amplitude of the modulated carrier-wave signal is controlled by an automatic power controller 16, amplified by a power amplifier 17 up to a specified transmission power, and then supplied through the antenna switch 4 to the low-pass filter 3 in which unnecessary frequency components are removed. The modulated carrier-wave signal with unnecessary frequency components removed is transmitted through the antenna 2.
In the arrangement of the receiver's high-frequency section mounted on the circuit board 1 as shown in FIG. 3, the high-frequency signal flows turning at right angles at the antenna switch 4, band-pass filter 5 and band-pass filter 7. Under this arrangement of the circuits, the input and output terminals of each of the band-pass filters 5 and 7 become close to each other, and thus the coupling coefficient between the signals flowing at the input and output terminals is great. Consequently, sufficient attenuation cannot be obtained as shown in FIG. 5 at (2). In addition, the output of the high-frequency amplifier 6 will be positively fed back to the input, so that there is the possibility that an undesirable oscillation is caused by the positive feedback. In other words, this deteriorates the reception sensitivity and the spurious-response ratio at the first image frequency or the like which are important characteristics of the receiver.
Similarly, the receiver's intermediate frequency sections also cause similar deterioration. That is, in the first intermediate frequency section, the attenuation in the band-pass filter 9 becomes insufficient and undesirable oscillation may occur in the first intermediate frequency amplifier 10 at the first intermediate frequency, leading to deterioration in the reception sensitivity and the spurious-response ratio at the second image frequency of the receiver. In the second intermediate frequency section, the attenuation in the band-pass filter 13 becomes insufficient and undesirable oscillation may occur in the second intermediate frequency amplifier 14 at the second intermediate frequency, leading to deterioration in reception sensitivity and other characteristics of the receiver.
Moreover, on the circuit board 1 shown in FIG. 3, the low-pass filter 5, high-frequency amplifier 6 and band-pass filter 7 are disposed close to the line on which a high-power signal is produced from the power amplifier 17, and the carrier-wave oscillator 20 and the automatic power controller 16 are disposed for away from each other so that signal lines connecting them become long. Therefore, the various circuits interfere with each other, probably causing their characteristics to degrade or causing self-oscillation upon transmission.
FIG. 4 shows the cross-sectional view of a radio apparatus including the circuit board 1. On both sides of the circuit board 1, there are mounted components such as a variable resistor 32 and a trimmer capacitor 33 which are necessary to adjust, large-height components 34 such as coils, capacitors, TCXO, various filters, power amplifiers and hybrid integrated circuits, small-height components 36 such as chip-type resistors, chip-type capacitors and thin-type integrated circuit chips. This circuit board 1 is fixed to a chassis or housing 30 with screws 31. Since the components such as the variable resistor 32 and trimmer capacitor 33 which are necessary to adjust are mounted on both sides of the circuit board 1 as described above, either some apertures for adjustment are required to be bored in the housing 30, or the components which are to be mounted on the lower side and necessary to adjust are provided with the capability of being adjusted from the bottom and apertures for adjustment are bored in the circuit board 1. The former case makes the cost of machining the housing 30 increase, while the latter case undesirably decreases the mounting area of the circuit board 1. Furthermore, since the large-height components 34 are mounted on both sides of the circuit board 1, it will be obvious that the circuit board 1 and the housing 30 must be separated by the height of those components or more. Thus, the height or thickness 35 of the whole radio apparatus increases to, for example, 17 mm, which is too thick for the radio apparatus to be used as a portable radio apparatus.
Thus, the conventional radio apparatus has the following problems with its packaging structure.
(1) Since the input and output terminals of certain filters and amplifiers of the receiver are close to each other, the coupling coefficients between the signals at the input and output terminals are large, so that the attenuation of the filters becomes insufficient and undesirable oscillation occurs in the amplifiers. Therefore receiver characteristics such as the reception sensitivity and the spurious-response ratio at the first and second image frequencies are deteriorated. PA1 (2) Since certain circuits of the receiver are disposed near to the line on which the high-power signal is produced from the power amplifier of the transmitter and certain circuits are connected together by long signal lines, the various circuits interfere with each other, such that the characteristics of the circuits of the receiver are degraded and self-oscillation is caused upon transmission. PA1 (3) Since the components which are necessary to adjust are mounted on both sides of the circuit board, they make not only the adjustment inconvenient but also the machining cost of the housing increase or the mounting area of the circuit board undesirably decrease. PA1 (4) Since the large-height components and small-height components are mounted on both sides of the circuit board, the whole circuit board thickness is increased and a useless space is created so that it is difficult to make the apparatus small.